Sema: Remove ConstraintSystem::SolverState::isRecordingChanges()

All but two remaining call sites can be changed to just check for a
non-null solverState, because we want to assert if we're inside
of an active undo.

The two places inside binding inference can check isUndoActive()
directly.

Author: slavapestov

include/swift/Sema/ConstraintSystem.h

@@ -2697,10 +2697,6 @@ class ConstraintSystem {
   /// we're exploring.
   SolverState *solverState = nullptr;
 
-  bool isRecordingChanges() const {
-    return solverState && !solverState->Trail.isUndoActive();
-  }
-
   void recordChange(SolverTrail::Change change) {
     solverState->Trail.recordChange(change);
   }

lib/Sema/CSBindings.cpp

@@ -1771,7 +1771,7 @@ void PotentialBindings::infer(Constraint *constraint) {
     return;
 
   // Record the change, if there are active scopes.
-  if (CS.isRecordingChanges())
+  if (CS.solverState && !CS.solverState->Trail.isUndoActive())
     CS.recordChange(SolverTrail::Change::InferredBindings(TypeVar, constraint));
 
   switch (constraint->getKind()) {
@@ -1945,7 +1945,7 @@ void PotentialBindings::retract(Constraint *constraint) {
     return;
 
   // Record the change, if there are active scopes.
-  if (CS.isRecordingChanges())
+  if (CS.solverState && !CS.solverState->Trail.isUndoActive())
     CS.recordChange(SolverTrail::Change::RetractedBindings(TypeVar, constraint));
 
   LLVM_DEBUG(

lib/Sema/CSGen.cpp

@@ -4930,7 +4930,7 @@ bool ConstraintSystem::generateConstraints(
     // Cache the outer generic environment, if it exists.
     if (target.getPackElementEnv()) {
       PackElementGenericEnvironments.push_back(target.getPackElementEnv());
-      ASSERT(!isRecordingChanges() && "Need to record a change");
+      ASSERT(!solverState && "Need to record a change");
     }
 
     // For a for-each statement, generate constraints for the pattern, where

lib/Sema/ConstraintGraph.cpp

@@ -77,10 +77,6 @@ void ConstraintGraph::addTypeVariable(TypeVariableType *typeVar) {
   // Record this type variable.
   TypeVariables.push_back(typeVar);
 
-  // Record the change, if there are active scopes. Note that we specifically
-  // check CS.solverState and not CS.isRecordingChanges(), because we want
-  // recordChange() to assert if there's an active undo. It is not valid to
-  // create new nodes during an undo.
   if (CS.solverState)
     CS.recordChange(SolverTrail::Change::AddedTypeVariable(typeVar));
 }
@@ -507,7 +503,7 @@ void ConstraintGraph::mergeNodes(TypeVariableType *typeVar1,
   auto &repNode = (*this)[typeVar1];
 
   // Record the change, if there are active scopes.
-  if (CS.isRecordingChanges()) {
+  if (CS.solverState) {
     CS.recordChange(
       SolverTrail::Change::ExtendedEquivalenceClass(
                         typeVar1,
@@ -560,7 +556,7 @@ void ConstraintGraph::bindTypeVariable(TypeVariableType *typeVar, Type fixed) {
     node.addReferencedVar(otherTypeVar);
 
     // Record the change, if there are active scopes.
-    if (CS.isRecordingChanges())
+    if (CS.solverState)
       CS.recordChange(SolverTrail::Change::RelatedTypeVariables(typeVar, otherTypeVar));
   }
 }